In operation, the paper machine rolls are subject simultaneously to mechanical strain, corrosion and wear. A cyclically varying load is typical of strain. Corrosion again results primarily from a relatively high operating temperature and from chlorides existing in the process environment.
Stainless and stainless duplex steels of various types are used at present as roll material. Duplex steel is characterized by a microstructure containing both ferrite and austenite. Equal volume shares are usually aimed at for these. Due to its two-phase microstructure, duplex steel features a good corrosion fatigue resistance.
Roll shells are nowadays made by a centrifugal method by casting or by welding of rolled sheet or by forging.
For example, printed patent publication FI-86747 presents a cast steel intended for paper machine rolls. It has the following composition: C max 0.10%, Si max 1.5%, Mn max 2.0%, Cr 25.0-27.0%, Ni 5.0-7.5%, Cu 1.5-3.5%, N max 0.15%, Mo max 0.5%.